Thermal growth of silicon dioxide film plays many key roles in the production and manufacture of IC semiconductor devices, and one of the most critical applications is serving as the MOSFET gate dielectric layer. When CMOS devices are scaled to gate lengths below 100 nm, they will require gate oxide equivalent thicknesses (EOT) of less than 2.0 nm. However, because direct tunneling current increases exponentially with decreasing thickness, it may not be feasible to use a pure silicon dioxide film with a thickness smaller than 2.0 nm. That is, it appears that a pure silicon dioxide film may not be suitable as a gate dielectric layer in sub-100 nm CMOS devices.
Several approaches have been suggested for resolving this issue, such as utilizing an oxynitride film instead of conventional silicon dioxide dielectric film. Current methods to prepare oxynitride include thermal nitridation and plasma nitridation, but both such methods have inherent limitations and constraints. For example, thinner oxynitride films can suffer from higher gate leakage. Constructing an ultra-thin gate oxide with sufficiently low leakage for advanced CMOS application is, thus, problematic, and is currently a critical issue.